1) Field of the Disclosure
The disclosure relates generally to assemblies and methods for hydraulic systems, and more specifically, to assemblies and methods for controlling hydraulic fluid temperature in hydraulic systems, such as an aircraft hydraulic system.
2) Description of Related Art
Aircraft hydraulic systems may be used to provide power for various operating components of an aircraft, such as wing flaps, thrust reversers, flight control surfaces, and landing gear mechanisms. Large, multi-engine aircraft may have several independent hydraulic systems. For example, two engine aircraft may have three hydraulic systems and four engine aircraft may have four hydraulic systems. Such aircraft hydraulic systems typically include engine driven or electrically driven pump devices mounted on each of the multiple engines. The pump devices pump hydraulic fluid through the aircraft hydraulic system at a high pressure. Aircraft typically operate at a pressure of 3000 psi (pounds per square inch), and some military aircraft and other aircraft may operate at a pressure of 5000 psi. Moreover, aircraft hydraulic systems for large, multi-engine aircraft may generate excess heat from the pump devices, such as in hot weather operations or conditions, which, in turn, may increase the temperature of the hydraulic fluid. Further, cold weather operations or conditions may decrease the temperature of the hydraulic fluid. Overheated hydraulic fluid, as well as hydraulic fluid that is not warm enough, may limit or restrict operation of the aircraft hydraulic system.
Known devices and methods exist for controlling the hydraulic fluid temperature in aircraft hydraulic systems. One such known device and method includes use and installation of a single fixed effect heat exchanger in an aircraft hydraulic system, such as, for example, in an aircraft fuel tank. However, for cold weather operations or conditions that require the hydraulic fluid be warmed up, use of such a heat exchanger may remove too much heat and may result in a cold hydraulic fluid that may be too cold to satisfy the required performance. Thus, operational restrictions and/or additional warm-up procedures may be required for cold weather operations. In some cases, design changes to the aircraft hydraulic systems may be required to up-size the hydraulic tubing and components in order to meet the requirement of hydraulic performance in cold weather conditions. Such increased size of the hydraulic tubing and components, in turn, may increase the overall weight of the aircraft which may result in a weight penalty and increased fuel costs.
Another known device and method includes use and installation of one or more thermostat control valves in an aircraft hydraulic system. However, such known thermostat control valves may require a thermal actuator which may be expensive, unreliable and may require a long lead time to develop. Moreover, such known thermostat control valves may not be capable of controlling heat dissipation based on a running condition of the pump device.
Accordingly, there is a need in the art for improved devices, assemblies, and methods for hydraulic fluid temperature or heat dissipation control in aircraft hydraulic systems that provide advantages over known devices, assemblies, and methods.